Method and apparatus for producing variable temperature with the aid of a cryoliquid

ABSTRACT

A method of producing variable temperatures with the aid of a cryoliquid, wherein the cryoliquid is throttled in a heatinsulated section at a point having poor heat conductivity, and at a distance from this point there is produced a variable temperature adjustable to values greater or equal to the boiling temperature of the cryoliquid, and apparatus for carrying out the method comprising a supply vessel for low-temperature gas, an evaporating device in which the low-temperature gas is arranged to be evaporated and at which the refrigerating output is arranged to be collected, and a regulating device for adjusting a predetermined temperature at the evaporating device, wherein the supply vessel is connected to a heat-insulated section, a heatinsulating flow resistor is arranged in the heat-insulated section, the heat-insulated section is sealed off by a gas-tight closure by which an evaporation chamber is defined, and a heating device with variable heating output is arranged at a distance from the flow resistor.

United States Patent [191 Gmelin et al. Oct. 7, 1975 [54] METHOD AND APPARATUS FOR 3,258,602 6/1966 Promish 62/514 PRODUCING VARIABLE TEMPERATURE 3,628,347 12/1971 Puckett 62/56 WITH THE AID OF A CRYOLIQUID [75] Inventors: Eberhard Gmelin; Ulrich yon Alpen, 52 j jg g agg Beaman both of Stuttgart, Germany or gen or I me [73] Assignee: Max-Planck-Gesellschaft zur Forderung der Wissensc'haften e.V., [57] ABSTRACT i g any A method of producing variable temperatures with the [22] Filed, 1 1974 aid of a cryoliquid, wherein the cryoliquid is throttled in a heat-insulated section at. a point having poor heat PP 9 ,523 conductivity, and at a distance from this point there is produced a variable temperature adjustable to values [30] Foreign Application Priority Data greater or equal to the boiling temperature of the cryollquid, and apparatus for carrying out the method Oct. 18, 1973 Germany 2352251 comprising a Supply Vessel for low temperature gas an May 2, 1974 Germany 2421102 evaporating device in which the 1Ow tmperature gas is arranged to be evaporated and at which the refriger- [52] US. Cl. ..5;;;,6622/526 ;.662;2l2% ating Output is arranged to be Collected and a regulat Int Cl 2 i 5/ ing device for adjusting a predetermined temperature J at the evaporating device wherein the supply vessel is [58] Field of Search 62/293 2 connected to a heat-insulated section, a heatinsulating flow resistor is arranged in the heat- R f d insulated section, the heat-insulated section is sealed e erences off by a gas-tight closure by which an evaporation UNITED STATES PATENTS chamber is defined, and a heating device with variable 1,659,663 2/1928 Nelson 62/293 heating output is arranged at a distance from the flow 2,996,893 8/1961 Goodenough 62/514 resistor, 3,188,824 6/1965 Geist 62/514 3,195,322 7/1965 London 62/514 7 Claims, 4 Drawing Figures US. Patent 0m. 7,1975 Sheet 1 of2 3,910,064

US. Patent Oct. 7,1975 Sheet 2 of2 3,910,064

FIGA

METHOD AND APPARATUS FOR PRODUCING VARIABLE TEMPERATURE WITH THE AID OF A CRYOLIQUID BACKGROUND OF THE INVENTION The invention relates to a method and apparatus for producing variable temperatures with the aid of a cryoliquid.

So-called cryostats are known with the aid of which a temperature lower than the ambient temperature can be maintained automatically, generally with great accuracy, over periods of time of any desired length. The lowest adjustable value of the temperature depends on the boiling point of the cryoliquid employed. If liquid nitrogen is employed, the boiling point is 77K, while in the case of liquid helium it is 4.2K.

In a known cryostat, the cryoliquid is supplied by way of a throttle valve, for example in the form of a needle valve, to an evaporator, by means of a pump and a control valve connected at the inlet side of the pump. A two-phase mixture, gas and liquid, is produced in the evaporator and a cooling effect is achieved by evaporation. The setting of the desired temperature is effected by appropriate adjustment of the throttle valve and the control valve or only by adjusting one of the two valves by means of a suitable regulating device. A cryostat of this kind is distinguished by comparatively high expenditure.

SUMMARY OF THE INVENTION The problem underlying the invention, therefore, is to effect a method of producing variable temperatures with the aid of a cryoliquid which can be carried into effect by comparatively simple means and is able to dispense with the use of mechanical moving parts.

In the method of the present invention, this problem is solved in that the cryoliquid is throttled in aheatinsulated section at a point having poor heat conduc' tion, and at a distance from this point there is produced by supply of heat a temperature adjustable to values greater or equal to the boiling temperature of the cryoliquid.

In the method according to the invention, in consequence of the supply of heat, a quasi-static vapour bubble is produced in the zone of the heat-insulated section behind the throttling point, which insulates this zone thermally from the cryoliquid, and this vapour bubble is used for cooling purposes. The quasi-static vapour bubble, which is under positive pressure, produces a phase boundary between the cryoliquid and the vapour bubble at the throttling point.

By varying the supply of heat in the zone of the quasistatic vapour bubble, any desired temperature can be adjusted with great accuracy in the bubble and outside the heat-insulated section. The application of the method according to the invention is independent of whether the cryostat consists of metal, glass, plastics or the like and includes the possibility of using all cryoliquids, such as helium, hydrogen, neon, argon, nitrogen, oxygen, etc.

The essential advantage of the method according to the invention consists in that for almost the same efficiency as in the case of the known cryostat only extremely small expenditure is required. Costly parts subject to wear, such as regulating valves, pumps and the like, are eliminated.

An embodiment of the method according to the invention provides that the heat-insulated section be sealed off under good heat-conducting conditions and be variably heatable in this zone. This measure, on the one hand, makes possible the problem-free supply of heat to the evaporation chamber between the throttling point and the heat-conduction seal or closures, and, on the otherhand, the desired temperature can thereby be adjusted on the outside in the region of the seal.

An apparatus for carrying the method according to the invention into effect comprises an arrangement with a supply vessel for low-temperature gas, an evaporating device in which the low-temperature gas is evaporated and at which the refrigerating output is collected, and a regulating device for adjusting a predetermined temperature at the evaporating device and is characterised in that the supply vessel is connected to a heat-insulated section, a heat-insulating flow resistor is arranged in the heat-insulated section, the heatinsulated section is sealed off by a gas-tight closure by which an evaporation chamber is defined, and a heating device with a variable heating power is arranged at a distance from the flow resistor.

In consequence of the supply of heat by the heating device, a quasi-static vapour bubble is built up under positive pressure in the evaporation chamber, as a result of which a phase boundary is set up between the liquid and the vapour bubble at the flow resistor. The flow resistor is of decisive importance, since the gas and liquid phases are separated thereat. The apparatus according to the invention enables any desired temperature above the boiling point of the cryoliquid employed to be adjusted in the zone of the quasi-static vapour bubble and in the immediately adjacent zone.

According to a development of the invention, it may be advantageous to design the flow resistor to be variable in flow cross-section. In another development of the invention it is provided that the closure consist of material having good heat conductivity, preferably copper. In this connection, it has proved to be advantageous to arrange the heating device in the closure. The heating device may be designed in any suitable conventional manner. Preferably, it is in the form of an electric heating device. An electric heating device offers the advantage of exact control of the desired supply of heat in dependence upon the desired temperature at the heat-conducting closure and inside the evaporation chamber. The heatconducting closure is advantageously provided with clamping or other retaining means to enable a sample to be flanged on.

As already stated above, the evaporation chamber must be heat-insulated with respect to the supply vessel and the cryoliquid, which is effected with the aid of a suitably designed flow resistor. On the other hand, this may be designed in any appropriate manner. According to a further advantageous development of the inven tion, it is provided that the heatinsulated section be a heat-insulated tube and that the flow resistor be formed by an insert body inserted into the tube and consisting of material having poor heat conduction and which is provided with one or more fine passages. Heatinsulating sintered material, for example, may be employed as such material. It is particularly advantageous, however, if the insert body consists of heat-insulating plastics, preferably polystyrene, polyurethane, etc.

According to another development of the invention, the insert body has as its periphery an encircling sealing surface which can be brought into sealing engagement with the inner face of the heatinsulating section. The above-mentioned boundary between the gas and liquid phases is formed in the sealing zone between the insert body and the inner face of the section.

Since the above-indicated material preferably employed for the insert body has unsatisfactory sealing properties, a development of the invention provides in this connection that, in particular when plastics is employed for the insert body, a sealing collar preferably consisting of polytetrafluoroethylene and copolymer of tetrafluoroethylene and hexafluoropropylene, polytrifluorochloroethylene or the like is placed around the insert body. 7

As likewise already mentioned hereinbefore, the throttling of the cryoliquid may be variable in order to ensure, for example, that the cryoliquid can be introduced directly into the evaporation chamber so that rapid cooling is produced.

To this end, it is advantageous to arrange the insert body movably and shape it conically for the purpose of varying the width of the gap between the insert body and the inner face of the heat-insulated section.

In another development of the invention it is provided that the heating device be arranged within the evaporation chamber or in or at one of the walls of the parts defining the evaporation chamber, preferably in the lower zone of the flow resistor.

It is true that an apparatus of this kind permits only the measurement of samples within the evaporation chamber. To make up for this, production is far simpler and makes possible a considerable reduction in the cost of manufacture. For example, it is not necessary as it is in the case of the above-described embodiments to make a difficult glass-to-metal seal to produce the closure of the evaporation chamber which has good heat-conducting properties in the above-mentioned embodiments.

According to a development of the last-mentioned embodiment, the heating device, which preferably has one or more electric heating coils, is arranged in a desired location within the evaporation chamber or at the end of an insert body which forms the flow resistor in the heat-insulated section.

In a further development of the invention, the gastight closure of the heat-insulated section likewise consists of heat-insulating material, preferably the material of the insert body, for example polystyrene, polyurethane, etc.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows diagrammatically the construction of a known cryostat;

FIG. 2 shows diagrammatically one embodiment of the cryostat according to the invention;

FIG. 3 shows in elevation part of an insert body for a cryostat according to FIG. 2;

FIG. 4 shows diagrammatically another embodiment of the cryostat according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS In the known cryostat shown in FIG. 1 a pump draws cryoliquid 11 out of a supply vessel 12 and by way of a needle valve 13 through an evaporator 14. A

control valve 15 is connected at the inlet side of the pump 10. The necessary vacuum chamber is indicated by a dashed line 16. The evaporator is a two-phase evaporator and the desired temperature is adjusted by adjusting the needle valve and the control valve with the aid of a suitable regulating device. The adjustment of the needle valve determines the throughput of liquid, while the control valve 15 determines the throughput of gas.

In the cryostat according to the present invention shown in FIG. 2, a supply vessel 17 is once again filled with a cryoliquid 18. The supply vessel 17 is followed by a tube-like section 19 the wall of which is formed of material having poor heat-conducting properties, such as glass, refined steel or plastics with poor heat conductivity. The free end of the section 19 is provided with a gas-tight sea] by means of a copper plate 20. Arranged in the copper plate is a heating coil 21 which can be connected to a voltage source (not shown). The voltage source is controllable so as to render possible a desired emission of heat by the heating coil 21. An insert body 22 in the form of a double cone is inserted in the upper zone of the section 19. The edge 23 of the body is designed to fit the inner periphery of the wall of the section 19, so that a sealing action is produced at this point. The insert body 22 consists of material having poor heat conductivity, preferably polystyrene, polyurethane or the like. The insert body 22, the cooper plate 20 and the section 19 define an evaporation chamber 24. A vacuum chamber is indicated by a dashed line 25.

By means of the heating coil 21, a temperature higher than the boiling temperature of the cryoliquid 18 is produced in the evaporation chamber 24, the cryoliquid leaking into the evaporation chamber in small amount over the edge 23. As a consequence, there is built up in the evaporation chamber 24 a quasi-static vapour bubble under positive pressure, which supports the cryoliquid 18 in thesupply vessel 17. The boundary between the gas and liquid phases is created in the region of the edge 23. In dependence upon the energy supplied to the heating coil 21, any desired temperature between the boiling point of the cryoliquid l8 and temperatures far above the ambient temperature can be achieved. The maximum value attainable for the temperature is determined by the properties of the materials employed for the cryostat. A sample may either be flanged on to the copper plate 20 or be introduced into the evaporation chamber 24. In the latter case, an access opening is required. Furthermore, a window may be provided in the section 19 to make optical checking and observation and optical measurements possible.

By shifting the insert body 22 upwardly, the sealing gap at the edge 23 can be enlarged in order to pass cryoliquid directly into the evaporation chamber 24 so that this chamber and the copper plate 20 are rapidly cooled.

If the insert body consists of polystyrene or polyurethane, it is advantageous to take special precautions for producing a sealing action between the insert body 22 and the inner face of the section 19. Therefore, for example, a sealing collar 26 consisting, for instance, of polytetrafluoroethylene and copolymer of tetrafluoroethylene and hexafluoropropylene may be provided. The sealing collar 26 is advantageously so designed that the outer sealing face is slightly conical in order to produce an effective seal.

The cryostat shown in FIG. 4 is essentially constructed like that of FIG. 2. Like parts are moreover provided with like reference numerals. There is a difference, however, in the heating arrangement. A heating coil 30 is arranged in the evaporation chamber 24 and by means thereof there is produced in this chamber a temperature higher than the boiling temperature of the cryoliquid 18, a small amount of which leaks into the evaporation chamber over the edge 23. As a consequence, there is built up in the evaporation chamber 24 a quasi-static vapour bubble under positive pressure, which supports the cryoliquid 18 in the supply vessel 17. The boundary between the gas and liquid phases is created in the region of the edge 23. In dependence upon the energy supplied to the heating coil 30 from the current source 27, any desired temperature between the boiling point of the cryoliquid 18 and temperatures far above the ambient temperature can be adjusted. The maximum value attainable for the temperature is determined by the properties of the materials employed for the cryostat. The samples are introduced into the evaporation chamber 24. An access opening (not shown) is required for this purpose. Furthermore, a window may be provided in the section 19 to make optical checking and observations and optical measurements possible.

A regulating device 28, which is not described in detail, is connected in the current path of the heating coil 30 for the purpose of adjusting the current supply to the heating coil 30 to any desired values.

By shifting the insert body 22 upwardly, the sealing gap at the edge 23 can be enlarged in order to pass cryoliquid directly into the evaporation chamber 24 so that it is rapidly cooled.

Instead of arranging the heating coil within the evaporation chamber 24, it may also be provided at the lower end of the insert body 22, as indicated by the reference numeral 29. The heating coil 29 can be supplied with current in the same way as the heating coil 30.

What is claimed is:

1. Apparatus for utilizing a cryoliquid to produce variable temperatures within an evaporation chamber comprising, in combination, a supply reservoir of cryoliquid having a bottom outlet, a thermally insulated expansion chamber in communication with said bottom outlet through a conduit passage and having a lower portion, a flow resistor mounted within said conduit passage controlling the flow of cryoliquid into said chamber in dependence upon the position of said flow resistor within said passage, and heating means within said chamber heating said chamber to produce a predetermined vapor pressure within said chamber for positioning said flow resistor to permit a predetermined flow of cryoliquid into said chamber to maintain a predetermined temperature within said chamber.

2. Apparatus for utilizing a cryoliquid as in claim 1 wherein said flow resistor includes sealing means cooperating with said conduit passage, said sealing means having a variable cross section in the direction of flow resistor movement.

3. Apparatus for utilizing :a cryoliquid as in claim 1 wherein said heating means comprises an electric resistance element within said chamber lower portion.

4. Apparatus for utilizing a cryoliquid as in claim 1 wherein said chamber lower portion includes a copper plate and said heating means includes an electric heating element within said plate.

5. Apparatus for utilizing a cryoliquid as in claim 1 wherein said flow resistor is of a conical configuration in the direction of flow resistor movement to vary the flow past said flow resistor in dependence upon the position of said flow resistor Within said conduit passage.

6. Apparatus for utilizing a cryoliquid as in claim 1 wherein said expansion chamber includes an upper cylindrical wall, said upper wall constituting said conduit passage receiving said flow resistor.

7. Apparatus for utilizing a cryoliquid to produce variable temperatures within an evaporation chamber comprising, in combination, a supply reservoir of cryo' liquid having a bottom outlet, a thermally insulated expansion chamber in communication with said bottom outlet through a conduit passage having a lower portion, a flow resistor mounted within said conduit passage controlling the flow of cryoliquid in said chamber, and heating means within said chamber heating said chamber to produce a predetermined vapor pressure within said chamber to maintain a predetermined tem perature within said chamber.

longitudinally movably 

1. Apparatus for utilizing a cryoliquid to produce variable temperatures within an evaporation chamber comprising, in combination, a supply reservoir of cryoliquid having a bottom outlet, a thermally insulated expansion chamber in communication with said bottom outlet through a conduit passage and having a lower portion, a flow resistor longitudinally movably mounted within said conduit passage controlling the flow of cryoliquid into said chamber in dependence upon the position of said flow resistor within said passage, and heating means within said chamber heating said chamber to produce a predetermined vapor pressure within said chamber for positioning said flow resistor to permit a predetermined flow of cryoliquid into said chamber to maintain a predetermined temperature within said chamber.
 2. Apparatus for utilizing a cryoliquid as in claim 1 wherein said flow resistor includes sealing means cooperating with said conduit passage, said sealing means having a variable cross section in the direction of flow resistor movement.
 3. Apparatus for utilizing a cryoliquid as in claim 1 wherein said heating means comprises an electric resistance element within said chamber lower portion.
 4. Apparatus for utilizing a cryoliquid as in claim 1 wherein said chamber lower portion includes a copper plate and said heating means includes an electric heating element within said plate.
 5. Apparatus for utilizing a cryoliquid as in claim 1 wherein said flow resistor is of a conical configuration in the direction of flow resistor movement to vary the flow past said flow resistor in dependence upon the position of said flow resistor within said conduit passage.
 6. Apparatus for utilizing a cryoliquid as in claim 1 wherein said expansion chamber includes an upper cylindrical wall, said upper wall constituting said conduit passage receiving said flow resistor.
 7. Apparatus for utilizing a cryoliquid to produce variable temperatures within an evaporation chamber comprising, in combination, a supply reservoir of cryoliquid having a bottom outlet, a thermally insulated expansion chamber in communication with said bottom outlet through a conduit passage having a lower portion, a flow resistor mounted within said conduit passage controlling the flow of cryoliquid in said chamber, and heating means within said chamber heating said chamber to produce a predetermined vapor pressure within said chamber to maintain a predetermined temperature within said chamber. 